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Chapter 7: nf-core Architecture, Linting & Community Modules

1 min read • Verified October 2026 • Peer-Reviewed Learning Resource
Tested Stacks: GATK 4.6.1 Samtools 1.21 Nextflow 24.10 Seurat v5.1 Python 3.12
Prerequisites: Basic Linux CLI & Sequencing Formats
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Chapter 7: nf-core Architecture, Linting & Community Modules

nf-core is a global community effort to curate peer-reviewed, best-practice bioinformatics pipelines built on Nextflow. Instead of writing custom processes from scratch, developers share standardized, atomic modules indexed in the central nf-core registry.

The nf-core Philosophy
  • One Pipeline per Problem: Avoid fragmented duplication (e.g. nf-core/rnaseq, nf-core/sarek).
  • Strict Portability: Every pipeline must run seamlessly across any POSIX environment, cluster, or cloud.
  • Continuous Automated Testing: Every commit is tested against full synthetic datasets using GitHub Actions.

1. Working with the nf-core CLI

# Install nf-core tools via pip or conda
pip install nf-core

# 1. List available community pipelines
nf-core pipelines list

# 2. Download a pipeline with all containers for offline HPC execution
nf-core download rnaseq --revision 3.14.0 --container-system singularity

# 3. Create a new standard pipeline template
nf-core create --name mygenomicspipeline --description "Custom variant caller"

2. Installing Atomic Community Modules

# Install pre-built, tested FastQC module into local repository
nf-core modules install fastqc

# Creates:
# modules/nf-core/fastqc/
#   ├── main.nf
#   ├── meta.yml
#   └── environment.yml

3. Parameter Validation with JSON Schema

nf-core pipelines enforce parameter integrity using a nextflow_schema.json file. Nextflow parses command line flags against this schema, rejecting invalid file paths or missing arguments before scheduling any compute tasks.

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Common Pitfalls & Troubleshooting Checklist

  • Java Heap Exhaustion (GATK / Picard): If processes terminate with java.lang.OutOfMemoryError, set your environment variable explicitly: export _JAVA_OPTIONS="-Xmx16g -Djava.io.tmpdir=/tmp".
  • Index Timestamp Mismatch: If tools complain that a BAM index is missing or out of date, regenerate with samtools index -@ 4 sample.bam.
  • Conda Channel Conflicts: Avoid ABI incompatibilities between bioconda and conda-forge by setting strict priority: conda config --set channel_priority strict.
  • Chromosome Naming Contamination: Always verify whether reference FASTA headers use chr1 or 1; divergent naming causes silent alignment drops.
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